With the increased emphasis on environmentally acceptable materials, solvent based adhesives have been rapidly replaced with either water-borne adhesives or hot melt adhesives (100% solids). Hot melt adhesives are comprised of thermoplastic polymers that generally maintain a level of mechanical load bearing capability up to near the flow temperature. These materials are generally crystalline polymers, however, block copolymers with a glass transition above room temperature are also employed. The hot melt adhesives are often highly formulated materials with tackifiers, plasticizers, waxes, resins, terpene resins, and the like, added to balance the processing and adhesive properties desired for the material. Important desired properties include low temperature flexibility, excellent adhesive strength, wettability, low viscosity and high stability at processing temperatures. Other desired properties include water resistance, adhesion to a wide variety of substrates, ability to accept a wide variety of modifications, open time and set time. In processing, open time, i.e., the time that the material is fluid such that the material can penetrate the substrate, is important as is the set time (the time required for a material to go from the fluid state to a solid state--often related to crystallization kinetics). Fast set times are required for high speed equipment. Low viscosity is required so that conventional equipment can be used to apply a very thin film or bead of material to the substrates to be bonded. Hot melt adhesives are generally applied between 150 and 190.degree. C. with viscosities of from 500 to 10,000 mPa-s and are expected to be stable for up to 24 hours at the application temperature.
The typical polymers utilized for hot melt adhesive applications include polyethylene, ethylene copolymers such as ethylene-vinyl acetate copolymers or ethylene-acrylic acid copolymers, polyesters, polyamides and styrene-butadiene-styrene block copolymers as well as their hydrogenated versions. As hot melt adhesives are continuing to replace the solvent based adhesives as well as other adhesive systems, e.g., reactive systems, additional materials are desired to meet the increasing demands for adhesive applications.
Hot melt adhesives based on olefin copolymers have been well documented in the patent literature for high pressure olefin copolymerization systems. These include ethylene copolymers with polar monomers such as vinyl acetate, acrylic acid, methyl acrylate, ethyl acrylate, mixed acrylates as well as ethylene terpolymers based on ethylene/polar monomer/carbon monoxide compositions.
JP 09031436 and JP 09031437 disclose hot melt adhesives comprised of copolymers of ethylene, CO, and unsaturated carboxylic acid esters combined with tackifier resins and waxes. EP 648801 notes a terpolymer of ethylene/alkyl acrylate/carbon monoxide as an adhesive for bonding furniture. WO 9318108 notes the use of CO containing ethylene co-and terpolymers in hot-melt adhesive formulations. Hot melt adhesives with good adhesion to various polymers based on ethylene/acrylates/CO terpolymers with hydrocarbon elastomers and tackifying resins were noted in JP 05017735.
Hot melt adhesives comprising ethylene terpolymers with CO or SO.sub.2 units along with tackifiers, plasticizers and waxes are noted in WO 9118043. U.S. Pat. No. 5,209,983 notes a blend of PVC, an ethylene/n-butyl acrylate/CO terpolymer and an ethylene/n-butyl acrylate/glycidyl methacrylate terpolymer is useful for bonding PVC to wood or other substrates for exterior use. U.S. Pat. No. 4,640,865 notes the use of a carbon monoxide containing polymer with a coating layer of a halogenated polymer as a heat sealable material useful for packaging. The ethylene co- and terpolymers noted above containing carbon monoxide were all polymerized using high pressure polyethylene polymerization procedures. These polymers are synthesized by a high pressure, free radical polymerization procedure that yields branched polymers. In the case of copolymers, the composition along the chain is random and the overall composition of the chain is based upon the reactivity ratio of the comonomer with ethylene. High pressure polyethylene homopolymer is typically 105-115.degree. C. whereas linear polyethylene has a melting point of 134.degree. C. (D. L. Beach and Y. V. Kissin; in Encyclopedia of Polymer Science and Engineering, Vol. 6, p. 410, John Wiley & Sons, New York, 1987). With the incorporation of comonomers such as n-butyl acrylate, acrylic acid, ethyl acrylate, vinyl acetate, and carbon monoxide, the melting point decreases rapidly and with levels of 10 wt % and more the melting points are generally below 100.degree. C. Compositions utilized for hot melt adhesives generally contain high amounts of comonomers and exhibit melting points well below 100.degree. C.
Olefin/CO alternating copolymers have been achieved using transition metal (palladium) catalysts for polymerization, see Drent, et al., J. Organometallic Chem., 417, 235(1991)). Ethylene/carbon monoxide copolymers have a melting point of 260.degree. C. Copolymers with minor amounts of propylene are employed to lower the melting point to increase the processability window as ECO copolymers have limited stability above 260.degree. C.
Several methods for preparing suitable catalyst compositions for the copolymerization of olefins with carbon monoxide to prepare linear alternating polyketones have recently been described in both patent and academic literature. Compositions may consist of a nickel salt, such as Ni(II) cyanide, in the presence of an anhydrous solvent. Numerous examples utilizing a Pd(II) salt with a strong organic acid in the presence of a bidentate chelating ligand which bonds in in cis geometry to Pd and optionally an oxidant have been disclosed. For example, U.S. Pat. No. 4,804,738 describes the use of Pd(II) acetate with at least 2 equivalents of trifluoroacetic acid and 1,3-bis(diphenylphosphino)propane to generate an active catalyst composition with or without a quinone, such as 1,4-benzoquinone, to increase catalyst mileage. Most polymerizations with acid promoted catalysts are performed in methanol as the reaction diluent which also serves as a telogen. One limitation apparent with acid promoted Pd(II) catalyst systems is the very low relative reactivity of C.sub.3 branched or higher aliphatic olefins relative to ethylene in solvents such as alcohols. Very low efficiencies and molecular weights are generally obtained for the polymers from such polymerizations. For example, U.S. Pat. No. 4,970,294 contains an example (Example 8) in which a mixture consisting of propylene and carbon monoxide was copolymerized in a composition consisting of palladium(II) acetate, methanol (solvent), copper para-tosylate and 1,3-bis(diphenylphosphino)propane. The reported polymerization rate was 0.3 kg copolymer/g palladium hour. The polymer had an average molecular weight in the range of about 1000 to 2000.
Recently described dicationic complexes which are substantially acid and alcohol free in the reaction composition are capable of producing polymers containing one or more olefins of C3 carbon atoms or higher with carbon monoxide at much higher overall rates and efficiencies than previously known. Generally the compositions consist of a transition metal source, such as Pd(II), which contains weakly or non-coordinating anions, a cis coordinating bidentate donor ligand and a telogen such as methanol. Examples of such catalysts have been disclosed by A. Lai Sen, T-W Inorg. Chem. (1984), 23, 3257-3258, and coworkers for the complex [Pd(CH.sub.3 CN).sub.4-n.(nPPh.sub.3)] (BF.sub.4).sub.2 (n=1-3), J. C. W. Chien, T. C. W, J. Poly. Sci: Part A, Poly. Chem., Vol. 30, 2735-2747 (1992), and coworkers improved the stability of the Sen system by addition of a cis chelating bidentate phosphine for the complex [PPh.sub.2 CH.sub.2 CH.sub.2 CH.sub.2 PPh.sub.2)Pd(CH.sub.3 CN).sub.2 ](BF.sub.4).sub.2 /CH.sub.3 OH and a series of cationic complexes have been reported in U.S. Pat. No. 5,554,777 based on the general formula (Pd(II)S.sub.4-x L.sub.x).sup.+2 (A).sup.-n.sub.y where S is a synthesis solvent, L is a mono- bi- or tri-dentate ligand, x is an integer from 1 to 3, A is a weakly or non-coordinating anion and n is 1 or 2 and y is 2 or 1.
Kinneberg and Armer (U.S. Pat. No. 4,871,618) note the use of a linear alternating copolymer of carbon monoxide and at least one ethylenically unsaturated hydrocarbon with a structure such that ethylene comprises at least 66 mole % of the ethylenically unsaturated hydrocarbon with melting points of&gt;175.degree. C. der Heide, et al. (U.S. Pat. No. 5,684,080) discuss an aqueous emulsion of a carbon monoxide copolymer with an olefinically unsaturated hydrocarbon and a curing agent composition which can be utilized for a wood adhesive. The examples note a propylene/carbon monoxide alternating copolymer of low molecular weight. U.S. Pat. No. 5,334,443 notes an adhesion promoting film composed of PVC and a low molecular weight carbon monoxide/propylene copolymer for coated fabrics. The utility of the alternating copolymers of olefins and carbon monoxide for hot melt adhesives has not been recognized in the open or patent literature.